The present invention relates to the manufacture of films, fabrics, and articles, and in particular to the manufacture of films, fabrics, and articles having (1) improved static electricity control; (2) improved corrosion inhibition; and/or (3) improved microbial inhibition characteristics.
Over the past three decades there has been increasing interest in the use of flexible, collapsible containers (a/k/a bulk bags) for handling flowable materials such as chemicals, minerals, fertilizers, foodstuffs, grains and other agricultural products, etc. The advantages resulting from the use of such receptacles include relatively low weight, reduced cost, versatility and, in the case of reusable receptacles, low return freight costs.
Fabrics are often utilized in the construction of flexible, collapsible containers where strength, flexibility and durability are important. Originally, such containers were fabricated from natural fibers; more recently, however, synthetic fibers manufactured from polypropylene, polyethylene or other polymeric materials have come into almost exclusive use. The popularity of synthetic fibers can be attributed to the fact that they are generally stronger and more durable than their natural fiber counterparts.
Even with the advances in fabric construction resulting from the shift from natural to synthetic fibers, fabrics in general possess qualities that render their use in certain applications undesirable. For example, the friction that occurs as dry flowable materials are handled by fabric receptacles tends to cause a significant build-up and retention of static electric charge within the receptacle. Discharge of the generated static electric build-up is often difficult, if not impossible, to control because fabrics are generally not electrically conductive materials. However, controlled discharge is imperative as static electric potential poses a significant danger of fire or explosion resulting from a static generated electrical spark.
In an effort to address the undesirable static electric discharge characteristic of fabrics, bag manufacturers covered one side of the fabric with a metallic foil-like layer. An adhesive was applied between the layers to affix the foil-like layer to the plastic fabric. The foil-like layer was generally comprised of aluminum or some other electrically conductive metal. The foil-covered fabric was then used to construct the receptacle, for example, with the foil side of the fabric comprising the interior surface. The foil layer provided an electrically conductive surface exposed to the flowable materials through which static electricity generated during material handling was discharged to an appropriate ground.
While adequately discharging static electric build-up if undamaged, the foil layer was susceptible to abrasion, tearing and separation from the fabric layer through normal use of the receptacle. For example, in filling, transporting and/or emptying of foil-covered fabric receptacles, abrasion between the flowable material and the foil layer tended to cause the foil layer to tear and/or separate from the fabric layer. The cumulative effect of such abrasion quickly reduced the effectiveness of the foil layer as a static electric discharge surface. Furthermore, tearing of the foil often resulted in a release of foil particles and flakes from the fabric, thereby contaminating the contained flowable materials.
To address the problems experienced with foil-covered fabrics, U.S. Pat. No. 4,833,008, issued to Norwin C. Derby, discloses a metalized fabric comprised of a woven plastic base fabric laminated to a metalized plastic film. The plastic base fabric is preferably a woven polypropylene fabric, and the plastic film is preferably an extruded polypropylene film. The plastic film is metalized through a vapor deposition process whereby a thin film of electrically conductive material is deposited on one side of the plastic film. The woven plastic fabric and the metalized plastic film are then laminated together through use of a plastic adhesive. Unlike foil covered fabrics, the thin conductive layer deposited on the plastic film is not subject to tearing or flaking; however, it is susceptible to chemical reactions.
U.S. Pat. No. 5,244,281, issued to Norwin C. Derby, of which this application is a continuation-in-part, discloses bags made from the fabric disclosed in the Derby ""008 Patent in combination with fabrics impregnated with anti-static compounds. The bags disclosed in the Derby ""281 Patent provide satisfactory anti-static capabilities. However, the fabrics of the present invention provide enhanced performance, and bags made from the fabric can be less expensive to produce.
Other recognized problems in the use of flexible, collapsible receptacles include corrosion and/or microbial contamination of the flowable material contained therein. In addition to the improved static discharge control, the present invention provides both enhanced corrosion inhibition and enhanced microbial inhibition over prior art practices.
In accordance with its broader aspects, the present invention comprises a method of manufacturing a flexible intermediate bulk container having predetermined performance characteristics comprising the steps of providing a thermoplastic resin, providing a chemical agent comprising the predetermined performance characteristic, mixing the resin and the chemical agent, forming the mixture into a woven fabric, cutting the fabric into a plurality of pieces, and joining the pieces to form a flexible intermediate bulk container having the desired performance characteristic. More particularly, the present invention comprises a flexible, collapsible receptacle (a/k/a bulk bag) for handling flowable materials which is fabricated from polymeric fabric and which provides (1) improved static control; (2) improved corrosion inhibition; and/or (3) improved microbial inhibition characteristics as compared with the prior art. The bulk bag itself may have any of the numerous designs known in the art such as those taught by U.S. Pat. No. 4,457,456 issued to Norwin C. Derby, et al. and U.S. Pat. No. 4,194,652 issued to Robert R. Williamson, et al., the disclosures of which are incorporated herein by reference.
In accordance with a first embodiment of the invention, the fabric utilized for construction of the bulk bag has improved static control characteristics. An inorganic static control additive distributed by the American Telephone and Telegraph Company (ATandT) under the trademark STATIC INTERCEPT(copyright) and available as an anti-static material/thermoplastic resin mixture from Engineered Materials, Inc. of Buffalo Grove, Ill., is blended in concentrations and quantities determined by the desired resistivity range of the finished bag product with a thermoplastic resin such as polypropylene or polyethylene in predetermined quantities based on the desired flowability and melt properties of an anti-static resin feedstock.
The STATIC INTERCEPT(copyright) anti-static material utilized in the practice of the present invention is superior to the anti-static material disclosed in U.S. Pat. No. 5,071,699, issued to Pappas"", et al., because the STATIC INTERCEPT(copyright) additive is inorganic, not fugitive, is effective in low concentrations and will not burn at extrusion temperatures.
The anti-static resin feedstock is extruded in at least six possible formats: (a) an anti-static layer extruded onto a polymeric fabric; (b) an anti-static layer extruded onto a polymeric film; (c) a co-extrusion comprising a layer of anti-static material and a layer of polymeric material; (d) an extruded anti-static film; (e) extruded anti-static tapes; and (f) extruded anti-static filaments.
The anti-static intermediate products identified above as (b), (c), and (d) are cut into long, narrow, thin strips (hereinafter referred to as xe2x80x9cslit anti-static tapesxe2x80x9d). The slit anti-static tapes and/or the extruded anti-static tapes, and/or the extruded anti-static filaments (collectively the xe2x80x9canti-static weavable membersxe2x80x9d) are woven into an anti-static fabric. Alternatively, one or more of the anti-static weavable members are combined with conventional polymeric tapes and/or filaments for weaving into an anti-static grid fabric. Any of the anti-static fabrics may then be cut and sewn to form an anti-static bulk bag. Additionally, anti-static filaments and/or anti-static tapes and/or anti-static threads may be used in the sewing of the anti-static bulk bag.
Alternatively, anti-static film may be laminated on various base layers using a thermoplastic resin as a bonding agent to create an anti-static sheet. The base layers may include (a) conventional film; (b) anti-static film; (c) anti-microbial film; and/or (d) anti-corrosion film. The anti-static sheets are then slit into anti-static tapes and woven as previously described into an anti-static fabric or an anti-static grid fabric.
It is previously known to add carbon to a thermoplastic resin mixture, and then to extrude the carbon-bearing resin mixture into a film, slit the film into tapes, weave the tapes into fabric, and use the fabric in the construction of bulk bags. However, experience with carbon-loaded resins in manufacturing anti-static fabric for bag construction has identified two serious problems. First, the fabrics are not sufficiently conductive as to provide anti-static protection until the resin mixture includes approximately 25% carbon. At that point, the resin mixture in the resulting fabric becomes almost totally conductive. Thus, it has heretofore not been possible to control the conductivity of the resin mixture and the resistivity of the fabric within a predetermined range as required by a particular application of the invention. Second, the inclusion of 25% carbon in the resin mixture distorts the nature of the polymeric material to such an extent that the resulting tapes and the fabrics woven therefrom do not retain the strength that they otherwise would have provided.
The lamination process may be used to form additional layered configurations including: (a) a conventional film laminated onto an anti-static fabric; (b) an anti-microbial film laminated onto an anti-static fabric; (c) an anti-static film laminated onto an anti-static fabric; and (d) an anti-corrosion film laminated onto an anti-static fabric. In accordance with conventional practice, micropores may be formed in the film layer to provide access to the fabric layer, if desired. The laminated fabrics thus produced may be cut and sewn into a bulk bag as previously described.
An anti-static, conventional polymeric, or anti-microbial liner may be installed in an anti-static bulk bag fabricated in accordance with any of the foregoing combinations of anti-static materials. Alternatively, an anti-static liner or an anti-microbial liner may be installed in a bulk bag fabricated from conventional polymeric fabrics. A cover made from conventional, anti-static, or anti-microbial material may be used in conjunction with a bag fabricated from conventional or anti-static fabrics. Conductive lift loops for use in fabricating anti-static bags may be fabricated from any of the aforementioned anti-static materials.
In accordance with a second embodiment of the invention, the fabric utilized in the construction of bulk bags has improved corrosion inhibiting characteristics. An inorganic corrosion control additive distributed by ATandT under the trademark CORROSION INTERCEPT(copyright), and available as an anti-corrosive material/thermoplastic resin mixture from Engineered Materials, Inc., of Buffalo Grove, Ill., is blended in concentrations and quantities determined by the desired corrosion inhibition range of the finished bag with a thermoplastic resin such as polypropylene or polyethylene in predetermined quantities based on the desired flowability and melt properties of an anti-corrosion resin feedstock. The anti-corrosion resin feedstock is then used in forming anti-corrosion fabrics, sheets and bulk bags in accordance with procedures similar to those described above in conjunction with anti-static fabrics, sheets and bulk bags. The corrosion inhibition additive reacts with and permanently neutralizes corrosive gases thereby cleansing air trapped in the bulk bag of substantially all corrosive gases.
In accordance with a third embodiment of the invention, the fabric utilized for construction of the bulk bag has improved microbial inhibiting characteristics. A microbial inhibitor additive is distributed by Microban Products Company of Huntersville, N.C., under the trademark MICROBAN(copyright). An alternative microbial inhibitor additive is distributed by HealthShield Technologies LLC of Westport, Conn., under the trademark HealthShield(trademark).
The microbial inhibitor is blended in concentrations and quantities determined by the desired microbial inhibition range of the finished bulk bag with a thermoplastic resin such as polypropylene or polyethylene in predetermined quantities based on the desired flowability and melt properties of an anti-microbial resin feedstock. The anti-microbial feedstock is then used in forming anti-microbial fabrics, sheets and bags in accordance with procedures similar to those described above in conjunction with anti-static fabrics, sheets and bulk bags. The microbial additive is mixed evenly throughout the polymeric material and migrates to the surface of the finished product on demand.
In accordance with a fourth embodiment of the invention, films, fabrics, and coatings are manufactured from polymeric materials including an anti-microbial agent. The preferred anti-microbial agent is xe2x80x9cHealthShieldxe2x80x9d(trademark), which is an anti-microbial compound combining silver with a naturally occurring inorganic ceramic that facilitates continuous, controlled release of ionic silver over an extended period of time. Films incorporating the fourth embodiment of the invention may be used, for example, as release sheets for hamburger patties and other food items. Films incorporating the fourth embodiment of the invention may also be used in the manufacture of liners for bulk bags. Fabrics incorporating the fourth embodiment of the invention may be used in the manufacture of bulk bags and in other applications. Coatings incorporating the fourth embodiment of the invention may be used in the manufacture of bulk bags and in other applications.